Similar to the related applications identified above, the invention disclosed here is designed to be used in conjunction with a rotary wire stripper of a type disclosed in U.S. Pat. No. 4,745,828, issued to Stepan, on May 24, 1988 (hereafter the '828 stripper). The '828 stripper is an excellent machine for stripping co-axial cables and other conductors where the wire's insulation is normally soft and thick. However, it is not particularly well-suited for cutting and stripping wires that are covered by one or more layers of thin, hard insulation.
For example, The Boeing Company, a well-known aircraft manufacturer, who is also the assignee of the invention disclosed here, uses one type of insulated wire having a center conductor that is covered by both an outer layer of soft insulation, and an intermediate layer of hard insulation. The hard insulation is typically very thin and glass-like in its hardness. Kapton (registered trademark) or multiple layers of fiberglass are typical materials used for this purpose.
Boeing uses other types of wires where the center conductor is first covered by a thin, very hard layer of Kapton (trademark), followed by an intermediate thick layer of soft insulation, and a thin outer sheath of fiberglass. Still another type involves a center conductor covered by a single thin layer of hard insulation with no intermediate layers.
The conventional blades used in conjunction with the '828 stripper cannot adequately strip the kinds of wires described above. A person having familiarity with the '828 stripper would know that it has diametrically opposed blades that circle and advance radially inwardly until the blades' edges cut through the insulation of the wire to be stripped. To be successful, the blades must cut the insulation as they are advanced inwardly, in order to prevent an accumulation of excess pressure between the blades and the wire's insulation. When the conventional blade encounters the type of hard, glass-like insulation described above, it cannot out through it as the blade advances. Instead, blade pressure on the insulation accumulates until the insulation is suddenly cracked in a crushing action. The uncontrolled pressure release created by this results in a poor stripping operation, especially when the wire's center conductor immediately underlies the layer of hard insulation. The sudden pressure release causes the blades to advance too far inwardly, thereby coming into contact with and nicking the center conductor.
Generally, and as a person skilled in the art would know, the wire's center conductor often consists of a plurality of small strands of copper twisted or braided together. Each strand is plated with a protective coating. Nicking one or more strands of the conductor removes this coating and creates a potential for long-term corrosion. Although this is usually not a problem that needs to be addressed in many manufactured products, it is a practical problem that cannot be ignored in aircraft manufacturing.
The invention disclosed here is designed to improve a rotary wire stripper, like the '828 stripper, so that it can be adapted to cut hard, thin layers of insulation without nicking the wire's conductor. As will become apparent, the invention is an improved blade design where the same blade is capable of cutting through and stripping both hard and soft insulation.